1. Field of Invention
The present invention relates to an interpolation digital-to-analog converter. More particularly, the present invention relates to an interpolation digital-to-analog converter for use in a source driver of a liquid crystal display.
2. Description of Related Art
For a conventional liquid crystal display, voltages applied to both sides of a liquid crystal layer fail to have a linear relation to light transmittance of the liquid crystal layer, thus when digital image data are converted into the voltages applied to both sides of the liquid crystal layer, a source driver needs to generate gamma voltages for gamma corrections of the applied voltages, so as to reduce color distortion shown on the liquid crystal display.
FIG. 1 illustrates a block diagram of a source driver in a conventional liquid crystal display. In the source driver 100, the shift register 110 enables the data register 120 sequentially from the left or right side, and the data register 120 is sequentially loaded with digital image data R, G, B according to the shift register 110 and its received clock signal CLK and then the digital image data are transmitted to the data latch 130. Next, the level shifter 140 adjusts levels of the outputs of the data latch 130, and the outputs of the data latch 130 are then converted into analog voltages by the digital-to-analog converter (DAC) 150. The analog voltages from the DAC 150 are transmitted through the buffer 160 to the liquid crystal display (LCD) panel, so as to drive the pixel array in the LCD panel.
FIG. 2 illustrates a gamma curve for gamma correction in a conventional liquid crystal display. As shown in FIG. 2, the horizontal coordinate represents digital image gray levels of a single sub-pixel, and the vertical coordinate represents gamma voltages corresponding to the digital image gray levels. For each sub-pixel, the light transmittance of the liquid crystal can be adjusted by changing the input voltages applied to both sides of the liquid crystal layer, such that the sub-pixel shows different illuminations. Furthermore, in order to prevent the liquid crystal molecules from deteriorating, gamma voltages with positive-polarity and negative-polarity can be alternately applied too both sides of the liquid crystal layer so as to protect the liquid crystal molecules.
However, in the foregoing conventional DAC 150, the required gamma voltages are usually obtained by employing resistor strings for generating dividing voltages, and this manner usually requires large areas to be designed and thus cannot effectively reduce the size of the circuit.